1. Field of the Invention
The present invention relates generally to a gasket for sealing a refrigerant compressor and, more particularly, relates to a metallic gasket covered with an elastic coating and adapted for providing a connecting portion between a cylinder block and end housings of a refrigerant compressor, and between high and low pressure regions inside the compressor, with a stable fluid-tight seal.
2. Description of the Related Art
In conventional refrigerant compressors such as swash plate and wobble plate type refrigerant compressors, a pair of front and rear cylinder blocks are axially combined together to define, at a connecting portion of both cylinder blocks, a swash plate chamber in which a refrigerant returning from an external refrigerating system is introduced to be compressed. The opposite ends of the combined front and rear cylinder blocks are closed by front and rear housings via front and rear valve plates and associated discharge valves. Each of the front and rear housings is provided with a radially outer suction chamber for the refrigerant gas before compression and a radially inner discharge chamber for the compressed refrigerant gas. The combined front and rear cylinder blocks are provided with a common central shaft bore for receiving therein an axial drive shaft on which a swash plate is fixedly mounted so as to be rotated with the drive shaft within the swash plate chamber. The combined front and rear cylinder blocks are provided with a plurality of axially extending cylinder bores in which double headed pistons operatively engaged with the swash plate via shoes are received to be reciprocated to implement suction and compression of the refrigerant gas, and to discharge the compressed refrigerant gas. Each of the front and rear valve plates is provided with suction ports bored therein and fluidly connected to the associated front or rear suction chamber. The suction ports of the front and rear valve plates are openably closed by suction valves. The front and rear valve plates are also provided with a plurality of discharge ports which are fluidly connected to the front and rear discharge chambers via the openable discharge valves and valve retainers which are formed as one part with gasket members interposed between the respective valve plates and the front and rear housings. The discharge ports of the front and rear valve plates are arranged to be in registration with the cylinder bores of the front and rear cylinder blocks to discharge the compressed refrigerant gas toward the front and rear discharge chambers through the discharge valves The front and rear suction chambers and the swash plate chamber are in fluid communication by suction passageways formed in the combined cylinder blocks. Similarly, the front and rear discharge chambers are fluid communication by discharge passageways formed in the combined cylinder blocks.
The outer framework of the refrigerant compressor provided by the above-mentioned combined front and rear cylinder blocks and the front and rear housings must be completely sealed against the atmospheric environment therearound. Further, since the compressor has, in the interior thereof, a low pressure region in which a suction pressure prevails, and a high pressure region in which a high pressure substantially corresponding to the compressed gas pressure prevails, the high and low pressure regions within the compressor must also be appropriately isolated from one an other. Thus, gaskets have been suitably incorporated in the compressor.
One of the typical gaskets assembled in a generally cylindrical body of a conventional refrigerant compressor is shown in FIGS. 6 and 7. Namely, a gasket 50 according to the prior art is made of a metallic plate coated with a thin elastic membrane. As best shown in FIG. 6, the gasket 50 includes an outer sealing portion 51 in the shape of a circular rim, and an inner sealing portion 52 in the shape of an annular rim arranged inside the outer sealing portion 51 and having curved portions extending toward and connected to the outer sealing portion 51. The outer sealing portion 51 functions to seal a circumferential region of the outer framework of the compressor against the atmosphere, and the inner sealing portion 52 functions to seal boundaries between the high pressure regions designated by "a" and the low pressure regions designated by "b", within the compressor body.
The gasket 50 further includes five radial ribs 53 between a central base rim 54 and the annular inner sealing portion 52 to function as valve retainers for determining an amount of opening of the discharge valves.
The gasket 50 has a ridge 61 arranged in the circular outer sealing portions 51 and a ridge 52 arranged in the annular inner sealing portion 52. These ridges 61 and 62 of the outer and inner sealing portions 51 and 52 of the gasket 50 are occasionally referred to as "beads", and are formed as smoothly curved projections having a continuously running apex, respectively (the apexes of the ridges 61 and 62 are shown by solid lines in FIG. 6, and these lines will be referred to as "an apex line", throughout the description hereinafter). The ridges 61 and 62 are trifurcatedly connected to one another at portions "A" and "B" where the outer sealing portion 51 and the inner sealing portion 52 are connected to each other. An enlarged view of the connecting portion "A" is shown in FIG. 7. The trifurcated connection of the ridges 61 and 62 of the outer and inner sealing portions 51 and 52 is achieved by a normal T-shape connection at the portion "A", and by an irregular T-shape connection at the portion "B". Nevertheless, the above-mentioned two trifurcated connections of the ridges 61 and 62 of the outer and inner sealing portions 51 and 52 have defects as set forth below. Namely, when the ridges 61 and 62 of the outer and inner sealing portions 51 and 52 of the gasket 50 are compressed between two mated parts such as an end of the front or rear cylinder block and the front or rear housing to be elastically deformed and collapsed, the mechanical rigidity of specified sections of the ridges 61 and 62, which are arranged adjacent to the connecting portions "A" and "B", is increased in comparison with the remaining sections of the ridges 61 and 62, and accordingly, the ridges 61 and 62 of the outer and inner sealing portions 51 and 52 of the gasket 50 cannot be elastically deformed uniformly which results in a failure to exhibit a stable sealing function at the connecting portions "A" and "B".